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Why does aileron response diminish as speed becomes slower, from slow-flight up to the stall? (In a light trainer)
Can someone phrase the explanation to this in simple words as you would explain to a student?

This is real easy, no explanation required:
Tell your student to stick their hand out the window of the car driving 25mph in the city and rotate it like an aileron.
Then have them do it on the freeway doing 60mph.
Feel the difference?  Did smaller movements produce larger effects at higher speeds?
Practical examples are typically more effective at driving a point home than a lot of words.

This can also be done in water for a more visual effect.

Or just say, "more speed, more energy".

I believe it's actually illegal to stick your hand out of a car, or "rest your elbow out the window", in Australia !

Legal disclaimer:  Don't do this in Australia.

To make the answer as simple as possible, an aerofoil will increase lift in two ways, either by going faster or increasing the angle of attack. When the aileron moves up or down it’s changing the shape of the wing and either increasing or decreasing the angle of attack. So, if you fly fast just a small aileron deflection will produce the necessary lift to raise the wing. Conversely, if the aerofoil is going slow the aileron will require a greater deflection to create a larger angle of attack for the same amount of wing movement. Hence at high speeds the aircraft will feel very responsive and at low speeds will feel unresponsive particularly as it approaches stall speeds. You should understand this is a very simple overview and there are many other aspects to consider.

Very simply, because the dynamic pressure drops as you slow down, making all aerodynamic controls more sluggish.
Aileron works by locally increasing the lift of one outboard wing and decreasing the lift of the other, thereby creating a torque or rolling moment. For simplicity, let's think that for every degree of aileron deflection, there is an associated increase and decrease in the local lift coefficient for TE down aileron and TE up aileron, respectively1.
You may remember that the total lift differential is proportional to the lift coefficient, but also to the dynamic pressure. You may also remember that dynamic pressure is proportional to the square of the true airspeed. Therefore, as you slow down, even though the lift coefficient differential remains more or less constant for the same aileron action, the total lift differential decreases as a square of the speed, and the same for the rolling moment.

1 The change in local lift coefficient is not constant across flight regime. As the AOA increases toward stall, significant nonlinear effect arises.

If the student is not grasping this simple concept I don't think using the words "coefficient" or "nonlinear" is likely to help.  ;)  Just sayin...

@MichaelHall I asked the same question when I was a university student.

Maybe I just stuck my hand out the window more than other kids...

The lift that is generated by an aileron at a fixed deflection (e.g. 5 degrees down) is proportional to the volume of air that is deflected downward per unit of time (e.g. per second). As speed is reduced the volume of air being deflected downward per unit time is reduced so the lift created by the aileron is also reduced and the aileron become less effective.

In the flight envelope you describe, the aileron response is affected by two factors:

the change in lift from the movement is related to the
speed of flight. As the speed reduces, the force diminishes, and,
when the wing stalls, airflow over the aileron is substantially
turbulent and no usable effect results from aileron movement.

This applies equally to other aircraft, not just light trainers. However, sophisticated fly-by-wire controls are often designed to not allow stalling and prevent the effect from being noticed under normal flight conditions.

why does aileron response decrease ... from slow flight up to stall.

Yes, controls definitely get more sluggish slowing down from cruise speed to slow flight, due to the reduction of aerodynamic force on their area.  From slow flight to stall, with ailerons, one must be aware of additional effects beyond reduction in airspeed.
Ailerons work by moving one up and one down.  All well and good until one goes to higher angles of attack.  There is a loss of effectiveness for the upturned aileron due to flow separation approaching stall.  This is compensated by increased angle of attack of the downtrend aileron, but it will stall first.  This is the dreaded "aileron reversal" that can lead to a spin.  Note that in the PARE spin recovery method, ailerons are nuetral.
From slow flight to stall, use your rudder and turn coordinated to stay safe.

You've quoted the question. Para 1 - confirming the question is a valid one and confirming it is actually the case. Para 2 - Explaining how ailerons work, and what happens during a stall. Going on to talk about the role of ailerons in a spin. Then how to recover from said spin. Para 3 - unrelated about control in slow flight. This is not a discussion forum, The answer box is for answers.

@Jamiec For the umpteenth time, you continue to accept vauge and inaccurate answers and utterly attack my contributions.  It should be clear to any aviation expert that "from slow flight to stall" is a very important and dangerous part of the flight envelope where improper use of ailerons can lead to loss of control.

Indeed, but that wasn't the question! And this isn't the answer.

And for the record, I do not "accept" answers on anything but my own questions. Your vote is as valid as anyone else's on what is a good answer or bad. That there are no downvotes on any of the other questions means you must not think that any of the others are not good answers to the question.

@Jamiec  I did include the other answers in my response "due to the reduction of aerodynamic force on their area" and tried to expand on a very key issue.  As one approaches stall, the upturned aileron loses effectiveness and actually produces more lift when the down turned one stalls.  So let's see how others feel.

For what it's worth, when a question is about aileron response decrease from slow flight up to stall, not from cruise up to slow flight, I think talking about what happens very close to stall forms an interesting and valid answer, even when that behavior is not strictly a decrease in respone (though one could easily argue that reversal is a decrease: -5 is less than +5)

@Jamiec: I don’t want to stick my nose into anything, but this answer came across my queue for review. It seems to me that both of you are correct to a point. Jamie is correct when he says that the answer includes extraneous information which is tangential to the original question. It should be more focused. Robert is correct to point out that, at increasingly high angles of attack, like those utilized in slow flight and near a stall, the upward deflected aileron often receives less airflow due to earlier airflow separation in the wake of the wing.

Easy - it's no different than the WHOLE WING exhibiting diminished response at low speeds! When you pull back on the yoke, that IS because you are getting diminished response from the wing. The ailerons likewise require more displacement for the same effect at low speeds compared to high speeds. If the student then can't grasp why the whole wing doesn't work at slow speeds, then you at least have uncovered the level of the student's intuition and understanding!


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Volume differences between intercom and outside communications
While flying I can hear my instructor in my headset talking no problem, but when they (and me) are speaking with ground/tower the volume in my headset is much lower. Is there anyway to increase the volume of the communications outside of the airplane?
Sorry, but different airplanes I fly in (172's) have different radios so I can't definitively quote the radio models and since it is happening in different airplanes its not tied to one specific plane or radio.
Based on the post
Do pilots have separate volume knobs on the radio panel? I think yesterday we had a Garmin GNS430, the others look similar also.

Welcome to Aviation! Radios have a volume control - your instructor should be able to show you. Why do you think the question you linked does not answer your question?

Just curious, why haven't you asked your instructor?

I did ask my instructor but they were uncertain of the reason why the difference in volume.

Don't forget you are paying them to teach you basic things like that!  My expectation would be a response along the lines of "good question, I haven't flow the GNS430 enough where I have needed to do this, but let's go look it up."  Or, if cost conscious, "do you want me to look it up before our next lesson, or do you want to read through the manual youself?"

@Alfie I'm happy to reopen this, but without specifics you'll get no better answer than the linked question. If you took a picture of the radio stack on one or more of the 172s you regularly fly I'm sure we can point out the relevant knobs to twiddle next time you're flying

Thanks, I appreciate all the input. I'll figure it out somehow. If I do I'll post here.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


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Calculating the horizontal distance the payload would travel with a parachute (horizontal drift)?
When you release a payload with the help of a circular parachute, and you want to find out the range in which it would land. And how would you find the descent gradient of the parachute?

The first thing to figure out is how fast your parachute will fall. From https://www.pcprg.com/rounddes.htm you can compute the falling velocity:
$$ V = \sqrt{\frac{2 W}{\rho C S}} $$
Where

$C$ is the parachute drag coefficient which is approx 0.75 for a parachute without holes or slits cut in the fabric; same value in both Metric and English unit systems

$S$ is the total surface area of the fabric used to build the parachute, plus the areas of the holes and vents cut in the fabric if present. The units of S are in square feet (English) or square meters (Metric). This definition is such that when vents are cut in the fabric, the value of $S$ remains the same but the value of $C$ becomes smaller.

$\rho$ is the air density

near sea level its value is given by
0.00237 sl/ft^3 (English units) and 1.225 Kg/m^3 (Metric)
near 4000 ft or 1219 m above sea level its value is
0.00211 sl/ft^3 (English units) and approx. 1.07 Kg/m^3 (Metric)

$W$ is the weight of the parachute + load, in pounds (English) or Newtons (Metric)

$V$ is the vertical descent velocity, here expressed in ft/sec (English) or m/sec (Metric)

You can either assume a constant speed all the way down, or make it a function of $\rho$.
With starting altitude and speed you can find the time it will take to fall.
Then you add the wind contribution. Multiply the wind speed by the descent time and you get the maximum range the parachute can reach.
The calculations will get a little mode tricky if you have a rho profile by altitude and wind speed profile by altitude.

Slightly complicated by the inertia of the load - it may be released with a significant horizontal speed and will not immediately adjust to wind shear.  At low rates of descent it’s possible for (even round) parachutes to get into a ‘flying’ state where there is some horizontal airspeed and the ‘chute acts an an aerofoil, slowing the rate of descent at the expense of horizontal airspeed.

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Is aerodynamics science still being discoverd?
Is aerodynamics science still being discovered(like mathematics for example) or everything has already done?

Better airfoils are still being developed, due in part to better computer modeling-- pertains in particular to high-performance sailplanes, and no doubt elsewhere as well-- maybe someone can take this start and develop into a real answer--

I believe they are still working on reducing jet engine noise.

Opinion based, however, all science is constantly evolving. Advancements are being made in lots of areas.

I'm pretty sure there is no field of study where everything has already been discovered.

Answering this question can be supported by citing the aerodynamic research projects currently being worked on. Which won't be opinion based. Voting to keep open.

Aerodynamics science is not a standalone discipline and involves many other aspects that are peculiar to it. In particular, only to cite some:

Fluid mechanics : fluid mechanics research is very extended, starting from experimental, until the numerical one. Related to it we have all the research related to math (Fluid dynamic equations' nature, specific solver algorithms...),  physics (fundamental fluid mechanics, wall cycle, turbulence...) and informatic (HPC architecture, computation efficiency...).
Design: new designs are considered and developed everyday. Remember for example that an airplane is an assembly of different systems that must cooperate (see the attached comic on the optimal plane by different groups). So engineers must find everyday new designs to satisfy this need of integration. One example is the Zeroe airbus concept, where hydrogen system must be suited in the body and innovative aerodynamic concept (like the blended wing body) are considered. Another case is the car racing world where every year there are new concepts (for basics see for example this book by Katz)
Drag reduction: Drag reduction research is always active (like the study and development of riblets, only to cite one). This can be related to basic fluid mechanics research of course.

These are some examples, but in general, as all the other science, Aerodynamics is always evolving as the disciplines related to it.

Research in aerodynamics has not stopped.  Just in the first ten days of 2022, over a thousand papers have been published.


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Before certified GPS, how much did a full IFR panel cost?
Certified IFR GPS navigators are expensive, but the price of even used HSIs and DME seem to bring some perspective to that cost. How much did a full IFR upgrade cost back in the day before GPS?

That's really difficult to quantify because in the 70s and 80s normal avionics were probably double/triple the cost, in constant dollars, of the same capability components today.  I have an ad for a crappy little Narco 1 1/2 nav/com marketed for basic GA airplanes called the Escort 110 from about 1975.  The thing, which was ultra basic, was 495 in 1975 dollars; 2500 today.  You might have paid nearly 1000 back then for a VOR receiver and head, 5 grand today.  So maybe someone spent 6-10k to put a full IFR panel in their 172 in 1980, or about 20-30 grand today.  So think the answer is, a LOT.

This should be easy to quantify, if anyone happens to remember: Before production ended in 1986, how much more did a Cessna 172 cost with a stock IFR panel, vs one with a stock VFR panel?

@rgfuller Easy? Costs $600 for a 1 year sub to Aerobluebook. They seem to be the only ones collecting this historical price info.


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Any idea what this 3-engine beauty is?
Can anybody identify this 3-engine flying boat moored on the ramp?

This is very likely to be a Savoia-Marchetti S.66
The front view is unmistakable (and pretty unique).

Here's another angle of it, almost certainly moored at the same place

Pre-War Italian flying boats are pretty distinctive, aren't they?

@ZeissIkon Almost everything designed by the Italians is distinctive ;)

Many thanks for your quick response - much appreciated.

@Tiger Instead of thanking in comments, you should accept an answer. Have a look at the tour.

Do any of the background features really match up between the two photos?

@quietflyer The dock itself in the foreground definitely seems to match.  You can even see that grate to the left of it in both shots.  It's harder to match the far shore, because a small change of angle gives you a completely different view, and it's likely a different focal length on the lens to boot, an effect magnified by distance.  I'd say the 2nd photo is pointed slightly to the right of the first, based on that sandbar in both shots, and the bridge, more visible in the 2nd shot than the first.

@qqjkztd The bridge does match up

Out of interest, Rex's Hanger (YouTube channel) covers more of the planes evolution and history in Italy's Weird & Wonderful Twin-Hull Flying Boats | Savoia-Marchetti S.55 & S.66

@quietflyer I'm sure that's the same place. Just like D.Hoffman said. I took qqjkztd's picture and marked some other features that match nice. Green - tree line near the bridge and a wide building just after the trees. Blue - two rightmost pillars and a tower behind them. Also, I'm pretty sure that this bridge is a railway bridge. You can see smoke from a moving train to the right (violet arrows, puffs, not yet dispersed by the wind; not a shape of a smoke from house/factory), and its roughly matches the bridge and shape of the terrain (the violet line, railways). -> https://ibb.co/HVmw6HN

@quetzalcoatl -- thanks for the note

I forgot a link, pasted now :)


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What is the average height above ground of the wings of a 777-200?
I have read somewhere that this is 18.4 to 18.6 m but not sure of the source. Is this information is correct?

The TAIL height (IE: how tall is the aircraft) is 18.5 m for the -200 and 18.6 m for the -300. That's nothing to do w/average WING height, which are not horizontal to the ground and bend upwards to tip so average is a meaningless #.

There isn't a single number for ground clearance. For the wing, Boeing publishes the height of the wing tip as between 16 ft 10 inches and 17 feet 4 inches. You can view all the other ground clearance numbers published by Boeing Aircraft for the purpose of airport planning here.

Thank you so much.


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What are all the squawk codes?
I love aviation and I love learning new things about it.
I was wondering if anyone knew all of the squawk codes and in particular what squawk 7500 means.

I can't add anything extra to the excellent comments already provided aside from the way I was taught to remember the main 3 codes. 75(00) - taken alive, 76(00) - in need of a (radio) fix, 77(00) - on my way to heaven.

When flying into Vancouver I hear you now can squawk 0420.

Related: Why is the range of transponder digits 0 to 7 rather than 0 to 9?

List of squawk codes

In the US https://www.faa.gov/documentLibrary/media/Order/FINAL_Order_7110_66E_NBCAP.pdf

@jean Be advised that list seems to be specific to the UK. I see several codes on there used for different things in other places.

Here is a list of all the squawk codes (there's 4096 of them). Very few of them have a specific fixed meaning. Probably the only three that always, globally, have the exact same meaning are 7500 (unlawful interference), 7600 (communication failure) and 7700 (emergency).
1200 is used for uncontrolled VFR in the USA. 2000 and 7000 are used for uncontrolled traffic in other areas, VFR or IFR depending on the territory. 7777 is used for test transponders.
If you want to know what squawk codes are used for, you should check out this question: How does ATC know if you have been assigned a squawk or not?
Anyway, without further ado:

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7352, 7353, 7354, 7355, 7356, 7357, 7360, 7361, 7362, 7363, 7364, 7365, 7366, 7367, 7370, 7371, 7372, 7373, 7374, 7375, 7376, 7377, 7400, 7401, 7402, 7403, 7404, 7405, 7406, 7407, 7410, 7411, 7412, 7413, 7414, 7415, 7416, 7417, 7420, 7421, 7422, 7423, 7424, 7425, 7426, 7427, 7430, 7431, 7432, 7433, 7434, 7435, 7436, 7437, 7440, 7441, 7442, 7443, 7444, 7445, 7446, 7447, 7450, 7451, 7452, 7453, 7454, 7455, 7456, 7457, 7460, 7461, 7462, 7463, 7464, 7465, 7466, 7467, 7470, 7471, 7472, 7473, 7474, 7475, 7476, 7477, **7500**, 7501, 7502, 7503, 7504, 7505, 7506, 7507, 7510, 7511, 7512, 7513, 7514, 7515, 7516, 7517, 7520, 7521, 7522, 7523, 7524, 7525, 7526, 7527, 7530, 7531, 7532, 7533, 7534, 7535, 7536, 7537, 7540, 7541, 7542, 7543, 7544, 7545, 7546, 7547, 7550, 7551, 7552, 7553, 7554, 7555, 7556, 7557, 7560, 7561, 7562, 7563, 7564, 7565, 7566, 7567, 7570, 7571, 7572, 7573, 7574, 7575, 7576, 7577, **7600**, 7601, 7602, 7603, 7604, 7605, 7606, 7607, 7610, 7611, 7612, 7613, 7614, 7615, 7616, 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+1 for the most comprehensive answer in the whole SE network ever.

Good answer, But I really dont see the value in listing out, verbatim, all the possible codes. You would have been better off describing how base 8 works.

@Jamiec Well yes, but ... this was more fun

I envision @J.Hougaard spending an hour and a half carefully typing out each digit, comma and space... Then I envision him copy/pasting from somewhere. :)

Oh octal. For reference, there are 4,096 codes because there are four digits, each counting up to 8. So 8^4 = 4096

@ymb1 Didn't seem to work, feel free to edit

I liked the non-horizontally-scrolling version better!

I felt a little bit bad about having upvoted a gratuitously over-literal answer (despite or maybe because I am  so often tempted to write this sort of answer) - The current version with a horizontally scrolling list seems a decent compromise.

@Jamiec he did ask for all the codes, and he got all the codes :)

Squawk codes are used by air traffic control to identify aircraft on the secondary surveillance radar. Flights are being given a squawk code by an air traffic controller, the pilot dials it into the radar transponder panel, and the radar reads that number out of the transponder and gives it back to the air traffic control system.
In the air traffic control system, information such as the flight plan, call-sign and given clearances can be associated to the radar track, and this is (partly) done based on the squawk code. The squawk code is a non-unique identifier. Typically flights that are under air traffic control are given a code that is unique in that control area. Non-controlled flights are given a generic code, so there may be many with the same code in a single air traffic control area. For example, for uncontrolled VFR in the USA code 1200 is used. On the oceans (where there is no radar control) code 2000 is used. Wikipedia has a list of many transponder codes and their uses. It does not contain all codes; for a list of all codes I refer the ultimate squawk code list by @J.Hougaard.
Three codes are designated as emergency code; their meaning is the same anywhere in the world:

7500: unlawful interference; used in hijacking situation
7600: lost communication; used when no radio contact can be established
7700: general emergency code

0400 is used by the last aircraft in a non-standard formation, until they're formed back up withing the 1 mile +/- 100 feet

In addition to the other great answers, you might be wondering why the squawk codes are the way they are — why each digit only goes up to 7 before rolling around to 0. I'm not an aviation expert but I do know about computing so I can answer this question. This is because the transponder is a simple electronic system sending binary information (ie what can be thought of as strings of just 1s or 0s). But long strings of 1s and 0s are hard for humans to remember, so we almost always represent binary strings in a different form.
Now, you may think binary is just a number, so we can just convert binary to our normal decimal numbers and use those. But this is actually quite tricky; because 10 isn't a power of 2, converting a binary number to decimal is non-trivial; it requires relatively complex circuitry to do so. If you think about this logically it makes sense; if I have a four digit decimal number, say 1000, that translates to 01111101000 in binary. But if I then change it to 1100, the binary is now 10001001100 — you see there have been changes throughout almost the whole number.
But if our base is a power of 2, like 8 for instance, we can split the number into useful chunks (for base 8, chunks of 3, because 2^3 is 8), which are entirely self-contained. For instance, base 8 (octal) 1000 translates to binary 001,000,000,000 (I'm using commas as digit separators so you can clearly see the groups of binary digits which correspond to each number), whereas octal 1100 translates to binary 001,001,000,000 — you see that each octal number corresponds 1:1 with a group of three binary digits. Octal 7777 would be 111,111,111,111.
Now, this is useful for both electrical circuitry, because it makes it simpler, and for humans who need to have a good understanding of how the binary works under the hood, because it's easier to do the mental mapping.
Octal was quite popular for a time, when the standard size of a group of binary digits was not generally fixed, so there's no reason it shouldn't have been a multiple of three. But in modern computing, we tend to use groups of eight binary digits as the smallest unit we generally care about, known as a byte. Three doesn't go into 8, so for that reason octal has generally fallen out of favour. Nowadays we tend to use hexadecimal (base 16), which uses numbers 0-9 and A-F, and each digit represents a group of four binary digits. But because of its age, octal lives on in aircraft transponders.

7500 hijack
7600 no radio
7700 emergency
If you really want to learn, reading the FAR and AIM will really get you up to speed:
http://www.faraim.org/
One might wonder why 8 and 9 are not used. I imagine it is to save on bits of data. Numbers 0 to 7 can be done in 3 bits - 000, 001, 010, 011, 100, 101, 110, 111. Numbers 8 and 9 need another bit: 1000, 1001. Saving a bit on each number simplifies the rotary knob a little bit, and saves 4 bits on the overall transmission. As it is, the four 0-7 digits allow 4096 codes in any one area, which might seem like plenty for any one controller to keep track of. Numbers 0000 to 9999 would mean really crowded skies!
Octal was popular for a while. 4 knobs to send 12 bits has been around quite a while. So even though the latest transponders use push buttons instead of knobs, the 8 numbers are with us for a while more. Maybe self flying taxis will drive up the range eventually.

In addition to those globally recognized special values, and locally valid special values (uncontrolled VR, IFR) you will be assigned the code by the ATC. They will usually assign you a code in sequence from some block they were assigned for this purpose. The exact procedure is highly specific to local procedures.
There is some very incomplete (mostly in the UK) list here http://www.flightradars.eu/squawkcodes.html
For example in the LKAA FIR (Czech Republic) it should work like this (completely unofficial, but likely fairly accurate, it is just an illustration):
0040 = search and rescue (if not assigned otherwise)
0041 - 0044 = search and rescue (assigned by ATC)
0045 = flights connected with human life saving (if not assigned otherwise)
0046 - 0047 = flights connected with human life saving (assigned by ATC)
0052 - 0053 = police helicopters daytime (if not assigned otherwise)
0054 - 0055 = police helicopters nighttime (if not assigned otherwise)
0056 - 0057 = flights of the civil aviation authority (assigned by ATC)
then

blocks for IFR flights, transit, arrivals, departures, domestic
IFR blocks inside local CTAs 0020 - 0037
VFR flights following airways 3330 - 3344
military flights - several blocks, depending on who is controlling
local flights

each airport has its own block, for example LKPR  3310 - 3317

For some information on how codes are allocated, here's the FAA's 7110.66 -
Beacon Code Allocation

Additionally, local air traffic facilities have reserved codes for local IFR and VFR traffic, as well as other codes that may function uniquely in their control environment. As an example, in JAX airspace a local VFR target (one not being handed off to an adjoining facility, will be assigned a 0400 code, local IFR a 0500 code. In ATL, 0100 is the local VFR set, but some of those codes are reserved for special flights, assigned only by ATC, and function uniquely to prevent AMAS alerts on runways.

Welcome to Av.SE!


text:
Is there a way for pilots to report difficulties and challenges experienced during a flight, to the next flight crew?
My question is reflected in the title - is there an official, international system for commercial pilots to report difficulties and challenges faced during a flight to the next and future crew? Ideally, such a system should also require the next crew to review recent entries into it. Does something like it exist and if so, how strictly is it followed?

system where pilots report difficulties and challenges experienced : that depends a) on regulations (honest response is "yes there is") b) whether they are actually followed (depends on several factors) and c) whether who experienced the problem considers it worth to point out (You won't report windshear in a paper every once you land in those conditions). It's not because it's written in an official paper that everyone applies, and it's not always the pilot to blame. We're talking about the entire world, not USA alone. If the weather radar is not available would you cancel the flight?

@KarlStephen Thanks, that makes sense. But I feel challenges that involve the plane losing altitude are certainly worth documenting. Hindsight is 20/20 of course.

I'm voting to close this question as off-topic because it is speculation about an accident whose investigation is still on-going, which is explicitly off-topic.

Close if you must, but the question is about the reporting system and the facts that are stated (presence of third pilot for example) are undisputed.

I don't think this is either opinion-based, nor accident speculation, as the discussion on MCAS, the Lion Air accident, and the Ethiopian Air accident, are merely preamble to what you're actually asking. I've made an edit to highlight this.

Thanks, the edit is an improvement.

I have removed all of the commentary from the question - with it, this question is borderline accident speculation which we don't support. Without it, this is IMO a good question.

The ASRS in the US?

"Difficulties" are hard to quantify. And it's questionable whether a difficulty experienced by one flight is even relevant to the next. Many difficulties are transient in nature (eg: weather, crew, cargo loading).
However, there is what is known as an Acceptable Defered Defect:

An identified aircraft defect which has been assessed as being within the requirements of the Minimum Equipment List (MEL) or Configuration Deviation List and has had rectification deferred within a specified limit. Also referred to as a CFD (Carried Forward Defect)

This is used to notify future aircrew of a specific aircraft of any defects which, although does not require the aircraft to be removed from service, may be relevant to its operation.
Pilots absolutely check this before every flight.

Thanks, this only holds for the United States?

Also, is this only inter airline or also intra airline if the other airline is flying the exact same model?

Last question, I'm sure most pilots check it, but are they required to check it by protocol?

I think this is talking about per aircraft defects.


text:
How is aircraft control positively transferred between pilot flying and pilot not-flying?
I am watching the video NTSB Animation Flight 1549 Hudson River Landing US Airways  (Youtube) and at 0:36 in the video, after the bird strike, you see the following dialogue:
HOT-1: my aircraft
HOT-2: your aircraft

I was curious to know what the formalities behind this is.  Could HOT-2 also claim the aircraft?

What you're quoting is the verbal portion of an important principle called Positive Exchange of Controls. This is a process of ensuring that someone (and only one) is always in control of the aircraft, and that there is no doubt about which pilot that is.
The best practice, taught to student pilots, is a three-stage handoff procedure:

Pilot A: You have the flight controls.
  Pilot B: I have the flight controls.
  Pilot A: You have the flight controls.

Pilot A is the Pilot Flying before the handoff, and Pilot B is the Pilot Flying after the handoff. In an emergency situation like the above, the captain (Captain Sullenberger, HOT-1, in this transcript) is responsible for the safety of the aircraft, and can assign control as they determine is best. Skipping the first line of the handoff is a reasonable way of making this happen  quickly, while not giving up much in terms of clarity. The two-stage transfer also can happen whenever someone, generally more experienced or in a teaching role, wants to be in control of the aircraft. As DJClayworth points out, a CFI will commonly take the controls in this fashion if they wish to demonstrate a maneuver - no imminent danger required.
HOT-2 refers to the "hot microphone", or recorded feed from the pilots' headset mics, from the first officer. Any time there's a change in Pilot Flying (if the captain gets up to go to the bathroom, for example), the controls should be exchanged in a manner similar to what we see above. If the FO feels that they should have the controls, they can always ask. There is no standard procedure for refusing the exchange of controls, but generally, if the Pilot Flying does not reply to the request with something along the lines of "You have the controls", then the exchange is incomplete, and the role of Pilot Flying has not changed.

One thing about that accident, if I recall correctly, was Capt Sullenberger gave control of the aircraft to the First Officer, so that as the senior pilot he could remain in overall command of all of the efforts, instead of 'simply flying the plane.'

FO Skiles was the PF for the departure, but Capt Sullenberger took the controls after the birdstrike: "At 1527:23, the captain took over control of the airplane, stating, 'my aircraft.'" - pg. 2 (pg. 19 of the PDF) http://www.ntsb.gov/doclib/reports/2010/AAR1003.pdf. You're correct that in many incidents, the captain will has the FO be PF so they can offload the workload of flying and focus on resolving the problem.

If the pilot in command is taking control, only the two-part handoff is necessary. This happens all the time when instructors take control from the student.

See also: Byzantine Generals Problem https://www.microsoft.com/en-us/research/publication/byzantine-generals-problem/

During the flight, there is a pilot flying (PF) who is in control of the plane, and a pilot not flying (PNF), who is monitoring communications, systems, navigation, and other things. In order to avoid confusion, or a situation where both pilots are trying to make different control inputs for the plane, it should be clear who is in control. If the PNF wants to take control of the plane, they must say "my aircraft", and the PF must acknowledge "your aircraft". The PNF now knows that they are in control, and they become the PF.
Generally, the captain would be more experienced pilot, and take control in difficult situations (like in the US Airways 1549 flight you linked to). However, if the first officer feels it necessary, he or she should be able to also ask for control of the aircraft.

Under what circumstances can the PF refuse the PNF's request. What phrases are used for refusal?

@RedGrittyBrick: That's an excellent candidate for a question. Why not post one?

@Eric: See http://aviation.stackexchange.com/q/5091/1289 - though NathanG's answer covers this a little bit. Maybe someone can come up with a comprehensive answer for this aspect.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Can a runway turnpad be used as a runway holding position?

Can a turnpad also be used as a runway holding position?

Since you're asking about regulations, please update your question to add which country and/or regulations you're interested in. This question has already been asked for the US, for example.

No, since you must have been cleared to enter the runway to be on the turn pad.  It is part of the runway.
From the point at which an aircraft is cleared to enter the runway, until it reports vacated or departs, the runway is occupied.

I'm not sure if ATC clearance would be the legal impediment; I've seen multiple a/c cleared onto the active in lots of small/crowded/strange airports (BVA,LTN) . I would think the lack of a holding marker on the ground would be a bigger issue, as I have effectivelly no reference of a line where my a/c will not inteferere with the one on arrival

@Radu094 Since you can't hold on an active runway, once cleared to enter, you must either vacate, take-off or abort. Regardless of how many aircraft, one or more means the runway is occupied.

well that's exactelly what (for instance) LTN does: with a clear to enter, backtrack, lineup and hold, then clear for intersection t/o for a second a/c behind us. Not sure of the legal implications, I was suprised originally, but now it seems common practice

@Radu094 Are you sure it's line up and hold, not line up and wait?  That sounds like a recipe for an accident.

from memory :" ..via Alpha clear to enter, backtrack, line-up and hold, there is departure ahead" ...I need to pay more attention to the radio...

@Radu094 - Here in the US, we can be given clearance from ATC to Line Up and Wait on the displaced threshold. It is quite common at one of our busier local airports while other aircraft are landing overhead. I would think that the term “line up and hold” would be avoided to avoid confusion. A better phrase would be to “Hold short runway xx. You are number x behind the [plane model]”. This particular airport has a pretty long displaced threshold where more than one aircraft can line up and wait.

@Simon - I occasionally fly into an airport (KRYW) that allows the turn pad to be used as a holding point. There are no taxiways to the AER and no displaced threshold. You have to backtaxi to the AER and immediately perform a rolling 180 on the runway surface in order to takeoff. If you want to stop at the AER to perform a run up, or use the turn pad to change directions, you have to completely exit the runway onto the turn pad. Once you are on the turn pad, re-entry onto the runway is not allowed without performing full runway hold short procedures.

@DeanF. my understanding of a "displaced threshold" means that there's a line painted on the runway and you're not allowed to land before crossing that line. Are you saying that your airport will put one or more aircraft on the runway prior to that line then have another aircraft land directly overhead? If so, that sounds incredibly dangerous and a violation of all sorts of rules.

@FreeMan - Interesting point. According to FAA JO 7110.65, some airfields can do it and some airfields can not. Then, in combination with FAA JO 7210.3BB, there appears to be time of day and weather restrictions as well. I wonder if having a nearly 1000 foot displaced threshold and taxi way all the way past the end of the displaced threshold play a factor in it as well.

@FreeMan - I suppose the thought process would be that controlling that space of the runway is less dangerous than if the displaced threshold were actually marked as a taxiway extension. It would also be less dangerous than some smaller airfields that have other vehicles access the AER when there is not a displaced threshold. I’ve seen automobile driveways as well as fence lines mere feet from the AER. Then there is the occasional industrial lawn mowing tractor. At least they usually carry airband radios and are in touch with the tower. Tower usually notifies landing traffic of their presence.

Not withstanding Simon's answer, the answer would be that it depends on the runway. The runway in the picture above has a displaced threshold and what appears to be a hold short (runway exit) line separating the runway from the turn pad.
The hold short line would indicate that the turn pad can be used as a place to hold while waiting for clearance for departure. With or without the displaced threshold, ATC could clear you to backtaxi onto the runway in order to reach the turn pad. Once there, you would begin holding short once the entire plane is beyond the hold short (runway exit) line. Holding there would not be an impediment to either arriving nor departing aircraft.
For departing aircraft, ATC could use the turn pad as extra room when having multiple aircraft performing Line Up And Wait maneuvers, preparing for departure. A scenario with a displaced threshold would put aircraft on the turn pad far away from the start of the Landing Distance Available.
Without a hold short line, ATC would not be able to hold the aircraft on the turn pad. Although, they could still issue a LUAW instruction by having the aircraft back taxi on the runway. It would probably then be up to the pilots discretion on where to perform a 180 turn around and where to hold as long as it is before the AER demarcating the beginning of the LDA.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Can a helicopter stand on the ground upside down on its rotor head?
From what I understand the rotor head needs to be strong enough to hold the craft weight hanging below it, and sounds pretty strong. The blades however look quite fragile (for a piece of metal).
In short, can a helicopter do something like this?

I found source of this GIF image: Escape to Witch Mountain (1975). This scene is around the 1h 19m mark. All hail @Peter Kämpf for identifying this copter as Hughes 500 which led me to list of copters in movies.
In the scene with humans and the Australian helicopter, a trained eye can spot the lack of a "green screen effect" (it's a 40-year-old movie!) so it seems this Hughes 500 was really put upside down! (Should we investigate it further to Movies.SE now?)

Followup on Movies.SE

That would be one hell of a joy-ride.

It's just a model.  And there were technologies to create scenes like this as special effects besides green-screen.  Compositing and matting could both be used.  Perhaps the biggest give away is that it's rotating the wrong way.

@simon American helicopter or European?

@Simon or from Australia, maybe? :)

@KorvinStarmast The rotor of an MD500 turns clockwise, therefore the  fuselage, when inverted, with the blades prevented from turning, the fuselage would rotate clockwise.

Green screen tech was invented in the 30s - around 70 years ago so it is not impossible to use green screen tech (back then it was called blue screen) 40 years ago.

@slebetman old green/blue screen is easily visible to naked eye, scenes with this copter flying upside down are example how horribly it can look :) Rotating scene looks too real for 40 year old special effect (that's why I always thought it was modern photoshop).

This certainly involved the use of magic.  The wizard set it on the ground after stopping the engine and rotors, which would be impossible in flight. Otherwise touching ground would be incredibly destructive.  Clearly the wizard put the spin on it himself, as @Simon discusses, the helicopter is incapable of this.

@PTwr - Even today I'd expect this to be a practical effect for most movies.

@slebetman - while both green and blue screens are both chroma-key techniques, the actual mechanism is very different.  Traditional blue screen usually separated the film into RGB colors and the removed the entire strip of blue (this caused problems during filming of the Superman movie, for obvious reasons - the suit had to be tinted green).  Modern green screen uses a computer to hunt for a rather narrow range of green (usually), plus modern compositing/editing tools allows for better tuning of the results, as well).

Australian? Do you mean American?

By the way, "Should we investigate it further to Movies.SE now?" - yes.   We don't know how it was done, but we do know what was not done.  What they did not do was take a real helicopter, turn it upside down and set it spinning.

@Simon Wait a sec, I though American rotors turned counter clockwise ... so inverted would turn clockwise, and thus the fuselage counter?

@KorvinStarmast  Er, cough, cough, yeh.  Er, too early in the morning, caffeine level still dangerously low.

@Simon I blame the coriolis effect.

@PeterMortensen it was a joke

Stand on its rotor head? yes, maybe. Spin? not for long.
The rotor hub and blades are quite strong and can take the helicopter weight at-least temporarily (leaving aside the balancing issue). The blades are designed to overcome stresses in flapping and can take the load. The rotor hub however, is not designed to take loads in this attitude (it is designed to lift the helicopter, and not push it) and its capability is an open question. You could put the helicopter upside down, but its going to be a brief affair with no guarantee that the parts will ever work again properly.
However, in case you want to spin the helicopter, you run into a number of issues. You could clamp the blades down and try to spin, but the rotor hub will struggle to take the load. The load path from the rotors to the fuselage is designed to take lifting loads and not this.
Helicopters are not designed for sustained inverted flight and as a result, the systems are not designed for anything like this. For example, the gearbox lubrication system isn't going to work for long in the upside down condition. The rotating control rods aren't going to take the gear box weight, let alone the helicopters'.
But first, the dynamic loads- helicopter systems below the rotor hub are not designed to take rotating loads, let alone the horribly unbalanced one like a fuselage. Even the lightweight helicopter blades are balanced to prevent and unsafe vibrations -in a case like this, the rotating fuselage would most likely tear apart the helicopter before anything else.

Fuel flow isn't going to work either, to the engines.

"not for long" - nice understatement!  I would be amazed if it managed even half a revolution.  Total destruction would be the outcome.

@KorvinStarmast How is that? The engines are right below the rotor, and the fuel is in the tail and below ("above") the passenger compartment; wouldn't gravity help? Or do you mean the centrifugal force will prevent it from flowing?

@cat Most fuel cells have the pumps in the bottom.  When you turn it upside down, you quickly end up with air in the fuel lines.  Fuel tanks are not pressurized, the fuel feed is pressurized once the pumps suck the fuel into them from the tank.

"Stand on its rotor head? Yes maybe". No, absolutely not. The capability of the rotor head to support the helicopter when upside down is not an open question. It cannot do it, the flapping hinges won't support this with a rotor that is not spinning.

This looks like a model that was carefully set up to spin.
First the facts: FAR part 27 regulates the design criteria for rotorcraft. Specifically, FAR 27.337 states:

The rotorcraft must be designed for—
(a) A limit maneuvering load
factor ranging from a positive limit of 3.5 to a negative limit of
−1.0 [snip]

So yes, contrary to the unsubstantiated claims in the highest-rated answer, the inverted rotor shaft can support the weight of the (most likely empty) helicopter. The center of gravity is very close to the rotor mast, and gyroscopic forces might even stabilise the fuselage long enough to film one full revolution, but still the clip is impossible to film with a real helicopter without breaking things. Look at the drawing of the Hughes 500 C, the type used in the clip, below:

Hughes 500 three-side view (picture source)
Clearly, the tail extends above the rotor plane, so something must be broken first before the fuselage is free to spin around. Next, everything must be carefully set up and the fuselage must be spun around somehow. This film was not made after an inverted touchdown - this is impossible with regular helicopters. From the linked page:

To enable a commercial helicopter to fly upside down, manufacturers
would need to make its rotor blades more rigid so as not to flex too
close to the main body of the helicopter (otherwise they could rip off
their own fuselage or other critical components). They would also need
to redesign the joint that connects the rotor blades with the rest of
the vehicle so it could bear the load of an upturned helicopter.
Finally, they would need to develop new controls to allow the rotor
blades to tilt downwards and reconfigure the engine so that fuel and
lubricants could be distributed properly while the helicopter was
inverted.

The page doesn't go into stability, but that would be another reason why this clip is not real. Flying upside down would be similar to balancing a broom on a fingertip.
Note that the FAR part 27 still demands a load that is equal to standing the helicopter on its head, regardless of the blades touching the body when loaded for -1g. Even though the helicopter cannot be flown inverted, the loads that would incur must still be tolerated, because they might happen in regular flight when a heavy gust hits the aircraft.
My explanation: Someone took his model helicopter, broke part of the tail off (note that the vertical part of it is missing in the clip!) and carefully balanced it on its rotor head. Mind you, he could even have fixed the rotor head to the ground with some tent stakes. There is enough structure inside of the hinges to facilitate this. Spinning it is easy, and no, there are no imbalances which would "tear the helicopter apart", especially not at such a leisurely rotation speed.

EDIT: Thanks to the invaluable help of @PTwr it is now clear that this is a scene from the 1975 Disney movie "Escape to Witch Mountain" in which two kids are chased by an evil millionaire. His helicopter in one scene flies and lands upside down. From www.rotaryaction.com:

… The chopper winds up flying upside-down and landing in that
position, still spinning, making the pilot and his passenger dizzy.

So it is a Hollywood special effect, and given the time of the movie (before CGI), this must have been shot with a scale model.

There is a huge difference between inverted flying and rotating standing on the rotor: Inverted flying is mainly about one thing: keeping the rotor head under the center of gravity. By moving the rotor head, not the center of gravity. When standing, that does not work, obviously.

@VolkerSiegel: Yes, that is what I meant with stability and balancing a broom on a fingertip.

Nice spot! Its Escape to Witch Mountain (1975). :)

@PTwr: Great find, thank you! I've never had known without your hint!

@PeterKämpf I would not find it without chopper name :) Until now I thought this was just some random photoshop magic.

The give away to the  fact it's either a model or special effect is that the fuselage is rotating the wrong way.

Unloading and negative g are a particular problem in twin bladed teetering helicopters, causing mast bumping. The Hughes 500 is not such a helicopter. The model may have been anchored into the ground, the blades of the model may even have been welded omto the rotor head for support - the real helicopter has flapping hinges, which hinge. Unless the rotor mast was buried 5 metres into the ground, it would topple over.

Your answer can be correct for a model, however the question is about a real helicopter.

@Koyovis: Does the FAR part 27 apply to models? Would tent stakes not be buried in the ground? I see no need for a 5m rotor mast extension. Please explain your comment.

The rotor blades don't support the fuselage upside down because of the flapping hinges. The rotor mast would have to be buried deep into the ground - but the actual helicopter rotor mast stops at the rotor hinge.

Nope, they cannot. There is a hinge in the rotor head that will make the helicopter want to topple over, it won't be spinning like in the video: it is not supported by the blades laying on the ground. Picture the blades not being there and you'll see how impossible it is to balance the whole construction on top of the rotor mast. And functionally (for this case) the blades are not there, they hinge up & down, see red circle in the picture underneath.

Some helicopters have a bearingless rotor head, dimensioned for making the fuselage follow the rotor disk while suspended in the air. Not for suspending the imbalance of a spinning fuselage when upside down: the CoG must be exactly in line with the rotor mast for this to occur, and real helicopters are designed with a useful CoG range.
When everything is up in the air, it might be conceivible for the helicopter to fly upside down if the collective could travel down as much as it can travel up, and if the fuselage could be supported like a broom on top of a hand, and would not spin. But not on the ground like in the video, no.
Update
Bearingless rotor heads have flexing beams instead of pure hinges, so the rotor head has some inherent stiffness to keep a fuselage upright when the helicopter is upside down. Some stiffness: when the rotor is spinning the centrifugal forces on the blades help in keeping them extended.
The vast majority of helicopters have flapping hinges or teetering hinges, both will make the helicopter flop over when in a situation like in the video. Yes the fuselage can stand on top of the rotor mast but the rotor mast won't stay upright, it'll hinge.

Actual rotor head of the Hughes 500. Check where the flapping hinge is.

I am pretty sure I've read helicopter capable of negative Gs is not possible and thinking about it I believe the flapping hinge will cause exactly the same problem as on the ground—the rotor is tilted by shifting lift with cyclic and the body hangs underneath it, so at negative Gs, the body would topple.

Yes indeed. They can withstand -1 g but in a normal position only, with the rotor on top :) Possible exception may be a hingeless rotor head, with a body balanced on top where nobody makes any wild movements.

Is this rotor head/hinge type from Hughes 500 this movie used (as model)?

@PTwr No this is from an EC 145 demonstrator. The reference book I have lists the Hughes 500 as having a hinge offset ratio of 12 cm: a classical hinged rotor that would topple over.

@Koyovis, the position does not matter. The time does. It can withstand -1G, so a sudden turbulence won't break it, but it can't fly that way for more than a second or two, because it would topple.

@PTwr The updated picture is similar to the Hughes 500 rotor head. The Flapping Hinge will prevent the rotor mast from staying upright.

@ Jan Hudec With a flying helicopter and a spinning rotor, the fuselage is lined up with the path of the rotor disk by a mechanical moment. Hinge offset rotors and bearingless rotors use the centrifugal forces of the spinning blades for that. These also have a limited ability to keep the fuselage upright when upside down. Only the teetering rotor would topple over immediately - their fuselages follow the rotor disk attitude as well, but this is caused by aerodynamic forces which work with some time delay in normal situations, but are too slow for upside down flight.

@JanHudec The Bo-105 can loop, but not do sustained inverted flight. Possibly other models can as well.

@jwenting, a loop is normally a positive G manoeuvre. The rotor is pulling on the body throughout.

@jwenting It cannot fly an outside loop.  Any sustained manoeuvre must be under +ve G.

According to the Web site, http://www.rotaryaction.com/e.html, the helicopter was a real Hughes 500 with extended landing skids.
I would assume that even if the frame was real, they would use a touch of movie magic to pull off the effect. To get the spin-rate right for a movie, I would assume they pulled the engine, used a rotary electric motor to control the exact rate of spin and balanced the helicopter to produce the effect.
Like others, my search for movie trivia came up blank. So I went to IMDB to see who the special effects people were and ask them the question. Unfortunately,
Art Cruickshank passed away 1983, Danny Lee passed away in 2014. Hal Bigger is listed as an uncredited special effects guy, but I could not find out if he was alive or a contact address.
If anyone wishes to contact the crew and ask them how they pulled off the effect, that's one way to get an answer on how it was done. I'll defer to others on whether or not you could do this with a real helicopter. My assumption is that under perfect conditions, you could power up and take off. But not without a modified Hughes 500.
IMDB Cast and Crew:
http://www.imdb.com/title/tt0072951/fullcredits?ref_=tt_cl_sm#cast

No. You have neglected to account for how drive systems work.
When the engines engage with the transmission, the blades begin to turn.  The sprag clutch/freewheeling unit is only oriented in one rotational direction and to catch.  If the load comes from the other direction of rotation, it disengages.   (See page 4-6 of the link).
In this particular case - beyond the problem of the fuselage being well out of balance - most helicopter's free wheeling units would not engage properly.
A more pressing difficulty would be that (if the engines would start) the engine would run until the problems with the fuel system arose.
Typical helicopter fuel systems rely on gravity feed into pumps in the bottom of the fuel cell, which then pressurize the fuel and get it to the engine.  When turned upside down means that the fuel will go to the new bottom (the top) and the air will go to the top (bottom) at which point the fuel pumps will start sucking in air instead of fuel.  If you get enough air into your fuel lines you can expect the engine to have trouble providing power to the rotor system.
(@JanHudec observed that the sprag clutch would likely engage, so part of the answer may be incorrect.  I may edit later after another estimate.  What is a freewheeling unit? It's what allows you to autorotate when you lose drive power from the engines).

A sprag clutch would have no problem engaging upside down, because for sprag clutch, the only thing that matters is the relative rotation and torque between the two elements, not which is actually turning and which is static. And the engine still turns the same way relatively to the gearbox. A centrifugal clutch would care, but helicopters don't use that (it behaves differently).

Of course the bearings will probably fail (because those have different strength against load in different direction) and the load will then break or dislodge the drivetrain that normally does not need to bear it, but that is different from the problem you describe.

Nice layman-friendly pdf. Thanks :)

@JanHudec Hmm, did I reverse direction on my little sketch with vectors and rotation?  (I did a quick 'back of the napkin' estimate.   It appears from your comment that this answer is wrong for me having done that backwards on my sketch.  I had the resisting force from the head going in the other direction.  Thanks for the comment, maybe this answer needs to be binned. (And Koyovis gave a better answer).

@PTwr Glad the link was helpful. :)  My answer may have a fatal defect, however, and will need another edit, or to be removed.  Make sure  to bookmark the link; it's for sure useful.

@JanHudec I had a mental model of the ground acting as a rotor brake, and I just realized where the extra vector came from that isn't there. Will probably delete later.

Can it...? Yes. But... practically No.
The points below explain why the answer is, strictly speaking, yes. But then, they explain why it,s not actually helpful in practice. Note how each case fails so fast that the technical properties of the helicopter are mostly irrelevant.
Can it stand on the rotor head?
Yes. The helicopter is in a nice equilibrium.
It's just that it is in an unstable equilibrium.
But the stiffness of the central drive shaft should be enough to keep it in balance for a while. And note that the drive shaft is somewhat tilted, not exactly vertical. If the pilot picks up his manual, searching for the right checklist, the helicopter will certainly fall over.
So, practically No.
Can it rotate on the rotor head?
Yes. The imbalance is no problem, when it starts slowly to rotate.
It will turn, but not a whole revolution. Probably not more one fourth of  a turn. There are some problems caused by the lacking rotational symmetry helicopters. When it just stands on the rotor, the orientation of the shaft is such that the center of gravity is above the rotor head. Depending on the amount of fuel, and the use of seat belts by the pilot, the center of gravity will be some centimeters away from the shaft axis. That means a rotation axis would need to be tilted by some degrees against the shaft.
So, practically No.
Can the rotor head handle it without just flying away?
Yes. The rotor head would be stabilized by being pressed into the ground.
The problem is with the other parts of the helicopter. All other parts. They would all fly away.
After rotating for some angle, the helicopter would move to the side of the center of gravity, rotating around the rotor head on an horizontal axis too. Before touching the ground, it will tilt the rotor head slightly, which would, because of the long lever, would move the rotor blades violently, if they would not break before. Soon later, the connection of the rotor head and the upper drive shaft would break, allowing the helicopter to crash.
Assuming we want more things to not fly away, like drive shaft, blades and pilot,
practically No.
The rotor head, pressed into the ground, just sits there, happily ever after.

Yes the rotor shaft is strong enough to support the fuselage, but what prevents it from toppling over?

In order to rotate with the CoG above the rotor, the helicopter would have to be perfectly balanced laterally and longitudinally.   No helicopter is built thus.  It would tear itself to pieces in a very short time as the fuselage toppled over and snapped the shaft.


text:
What FAA requirements exist for electronic ignition systems on piston engines?
Most GA piston aircraft still use dual magnetos for their ignition system, but there are some STC kits available to add electronic ignition to common piston engines, and new aircraft often come with FADEC systems.
Are there particular FAA requirements for electronic ignition systems?
If so, what are they and how can you demonstrate compliance?

The ignition requirements are pretty straight-forward:

§23.1165   Engine ignition systems.
(a) Each battery ignition system must be supplemented by a generator
  that is automatically available as an alternate source of electrical
  energy to allow continued engine operation if any battery becomes
  depleted.
(b) The capacity of batteries and generators must be large enough to
  meet the simultaneous demands of the engine ignition system and the
  greatest demands of any electrical system components that draw from
  the same source.
(c) The design of the engine ignition system must account for—
(1) The condition of an inoperative generator;
(2) The condition of a completely depleted battery with the generator
  running at its normal operating speed; and
(3) The condition of a completely depleted battery with the generator
  operating at idling speed, if there is only one battery.
(d) There must be means to warn appropriate crewmembers if
  malfunctioning of any part of the electrical system is causing the
  continuous discharge of any battery used for engine ignition.
(e) Each turbine engine ignition system must be independent of any
  electrical circuit that is not used for assisting, controlling, or
  analyzing the operation of that system.
(f) In addition, for commuter category airplanes, each turbine engine
  ignition system must be an essential electrical load.

What about aircraft not certified under Part 23?

@egid His question is about "GA piston aircraft" so I doubt that many of them would be certified under anything else.  :)

There are a ton of GA piston designs certified under CAR part 3, both before and after 1965 when Part 23 was created.

@egid I know nothing about CAR....  ;-)

I think we can consider CAR 3 and FAR 23 "roughly equivalent" for these purposes (I'm fairly certain the FAA would view any modifications/retrofits in the context of FAR 23, even if the original type certificate was issued under CAR 3).